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IS 5305 (1969): Method for volumetric determination ofphosphorus [CHD 1: Inorganic Chemicals]

IS:5305-l!J@

fndian Standard ( Rmffirm* ‘983)

METHOD FOR VOLUMETRIC; DETERMINATION OF PHOSPHORUS

( Second Reprint JUNE 1988 )

-. UDC 543.?4:546.18

@I CoPyi& 1969

BUREAU OF INDIAN STANDARDS MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MAR0

NEW DELHI 110002

December 1969 .

Is:5305-198)

Indian Standard METHOD FOR VOLUMETRIC

DETERMINATION OF PHOSPHORUS

Chemical Standards Sectional Committee, CDC 1

Chainnan DR K. L. Mouno~u

Morning Side, Camel’s Back Road, Mussoorie

Manbsrs &Pm-%

SIUU V. J_ BARRE Central Revenues Control Laboratory, New Delhi SBRI K. S. SU~RAMANIAN ( Al&mate )

SHRI V. M. BHUCHAR National Physical Laboratory ( CSIR ), New Delhi

SHRI S. K. BOSE National Test Nouse, Calcutta

Ca~snsr & METALLURGIST, CEN- Railway Board ( Ministry of Railways ) TRAL RAILWAY, PAREL, BOMBAY

ASSISTANT DIRECTOR (.MET ), RDSO, ’ CIWITARANJAN (Alternate)

DIRECTOR Central Agmark Laboratory, Nagpur

DRS. GHOSH IS1 Laboratory, New Delhi

DR N. JAYARAHAN Fssen & Co, Bangalore SHRI M. R. G. SHARMA ( Al&mate )

DR S. M. KAJI Italah Pvt Ltd, Bombay SHRI S. S. HONAVAR (Alternate)

DRN.M. KHANNA

DR H. S. MAHAL

SHRX S. N. hkTRA

DR V. S. K. N~UR SHR~ S. BAGCHI ( Altcmati )

DR V. SADASIVAN

DR B. R. SANT

DR T. P. PRA~AD ( Alfernate )

DR E. R. SAXENA Da ZAFAR ZAMEEL ( Alternate )

SHR~ M. L. SETH

Central Drug Research Institute ( CSIR ), Lucknow

Maharashtra State Forensic Laboratory, Bombay

Central *Food Laboratory (Ministry of Health, Fad~x;ta Planning & Urban Develepment ),

Bird & Co Pvt Ltd, Calcutta

Bombay Municipal Corporation, Bombay

Regional Research Laboratory I CSIR ), Bhubaneswar

Regional Research Laboratory ( CSIR ), Hyderabad

Institution of Chemists ( India), Calcutta , \ SHRI SHYAMDAS BAGCHI ( Altemarc )

( Continwd on page 2 )

BUREAU OF INDIAN STANDARDS MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

r- 1

NEW DELHI 110002

18:x305-1969

( Continuedfrom page 1 )

Members R.+resenting

DR R.S. SRIVASTAVA

DR P. R. SWHARAMAN

SHRX L. R. SUD SHRI S. G. KAJREKAR (

DR J. N. TAYAL

DR R. T. THAMPY

SHRI D. DAS GUPTA, Director ( Chem )

Swasthya Scwa Nideshalaya, Lucknow

National Chemical Laboratory ( CSIR ), Poona

Ministry of Defence ( DC1 ) Alternate )

Central Indian Pharmacopoeia Laboratory, Ghaziabad

Shri Ram ‘Institute for Industrial Research, Delhi

Director General, BIS ( Ex-o#cio Mrmbcr )

Secretary

SHRI S. ARAVAYUDHAN

Assistant Director ( Chem ),BIS

2

IS:5305-1969

Indian Standard METHOD FOR VOLUMETRIC

DETERMINATION OF PHOSPHORUS

0. FOREWORD

0.1 This Indian Standard was adopted by the Indian Standards Institution on 18 September 1969, after the draft finalized by the Chemical Standards Sectional Committee had been approved by the Chemical Division Council.

0.2 In the determination of phosphorus, it is generally required that the phosphorus shall be present as orthophosphate. Phosphorus in minerals is inuariably present as orthophosphate and so requires no special treatment. In the case of organic phosphorus compounds, initial decom- position may sometimes be accomplished by treatment with nitric and perchloric acid or heating with nitric acid and potassium permanganate If these fail, then more drastic treatment, such as heating with nitric acid in sealed tubes or fusion with peroxide may be necessary. Use of sulphuric acid for making solution of the sample shall be avoided.

0.3 When calcium, iron, vanadium, titanium, zirconium, tungsten, talurium, silicon, selenium and arsenic are present, they interfere and retard the precipitation of phosphomolybdate. Interference of calcium and iron may be overcome by either precipitating phosphorus as magnesium ammonium phosphate in <presence of much ammonium citrate or separating phosphorus from these elements by precipitation as ammonium phosphomolybdate in acid media, then the precipitate dissolved in alkali and phosphate precipitated as magnesium ammonium phosphate. Interference of elements like vanadium, titanium, zirconium, etc, may be overcome by employing a large excess of molybdate reagent and allowing a longer period for precipitation. Silica and arsenic may be eliminated by using tartaric acid, suitably modifying the method.

0.4 The method of precipitation of phosphorus as ammonium phospho- molybdate has been used for many years and is still used, especially in the analysis of minerals, fertilizers and ferrous and non-ferrous metals, It is of almost universal application.

0.5 Although gravimetric determination by precipitation of phosphorus as magnesium ammonium phosphate, direct titration of orthophosphata ( phosphoric acid ), direct titration of pyrophosphates (pyrophosphoric acid) and titration of the reduced acids of phosphorus are still in use for routine analysis, the ammonium phosphomolybdate method and the

3

P

ISr5505-1969

quinoline phosphomolybdate method are good for routine analysis so they have been recommended and prescribed in this standard.

0.6 In reporting the result of a test or analysis made in accordance with this standard, if the final value, observed or calculated, is to be rounded off, it shall be done in accordance with IS : 2-1960*.

1. SCOPE

1.1 This standard prescribes the method for the volumetric determination of phosphorus by using (a) ammonium molybdate, and (b) quinoline.

NOTE - The method is intended aa a general analytical method and does not apply to metal analysis whete limits for various interfering elements and/or radicals are prescribed.

2. &UALITY OF REAGENTS

2.1 Unless specified otherwise, pure chemicals and distilled water ( see IS : 1070.1960t ) shall be used in tests.

NOTE - ‘ Pure chemicals ’ shall mean chemicals that do not contain impurities which affect the results of analysis.

3. METHOD A - AMMONIUM PHOSPKOMOLYBDATE METHOD

3.0 Outline of the Method - The solution of the sample is treated at about 45°C with a large excess of ammonium molybdate solution in the presence of nitric acid. The precipitated ammonium phosphomolybdate is suitably washed with dilute potassium nitrate solution, dissolved in an excess of standard sodium hydroxide and the solution of sodium hydroxide is titrated with standard hydrochloric acid. The phosphorus is calculated from the volume of sodium hydroxide solution that was required to react with the ammonium phosphomo1ybdat.e.

3.1 Reagent8

3.1.1 Phenolphthalein Indicator-See Table 1 of IS : 2263-1962:.

3.1.2 Dilute’J\rric Acid- 10 percent ( v/vi> and 40 percent ( v/v ),

3.1.3 Ammonium N&ate - 10 percent ( w/v ).

3.1.4 Standard Sodium Hydroxide Solution - Carbonate-free, 0.1 N ( see

IS : 2316-1968s ).

3.1.5 Standard Hydrochloric Acid- 0.1 N ( see IS : 2316-1968s).

*Rules for rounding off numerical values ( rsuised ) .

tSpecification for water, distilled quality ( mired ).

SMethods of preparation of indicator solution for volumetric analysis.

OMethods of preparation of standard solutions for calorimetric and volumetric analysis ( mired ) .

4

l!s:5385-1969

3.1.6 Ammonia - sp gr O-90.

3.1.7 Potassium N&ate Solution - 1 percent ( w/v ).

3.1.8 Ammonium Molybdate Solution - Add solution A ( 3.1.8.1) slowly and with constant stirring to solution B ( 3.1.8.2 ) kept cool in a cold waterbath. Add 10 ml of ammonium phosphate solut;on ( one gram per litre ) and keep the solution at least for 24 hours. Filter the solution through What- man filter paper No. 1 before use.

3.1.8.1 Solution A - Dissolve 100 g of molybdid acid ( MOO,, 85 percent ) or 118 g of ammonium mo!ybdate in a mixture of 145 ml of concentrated ammonium hydroxide and 270 ml of water. Cool the solution.

3.1.8.2 Solution % -Add 490 ml of concentrated nitric acid to 1 150 ml of water and cool.

3.2 Procedure -Take in an Erlenmeyer flask a clear solution of the material, prepared as prescribed in the relevant material specification containing 5 to 10 mg of phosphorus present as orthophosphate in about 100 ml of the solution. Add 10 ml of 10 percent nitric acid and 10 ml of 10 percent ammonium nitrate. Dilute to about 200 ml and heat to 45°C. Add ammonium molybdate reagent in small quantities with stirring to precipitate all of the reagent hp

hosphate present. After the precipitate formed on addition as settied, test for completion of precipitation and then add

further 10 ml of reagent ( generally 20 to 30 ml will be sufficient ), Stopper the flask, shake vigorously for 5 to 10 minutes and allow to stand for 30 minutes. Filter through a Whatman No. 40 filter paper or paper pulp. Wash the flask and the precipitate a few times with 1 : 50 nitric acid and then with 1 percent potassium nitrate solution until a portion of the filtrate does not decolourise 1 ml of water containing 1 drop of 0.1 N sodium hydroxide and 1 drop of phenolphthalein. precipitate in the original flask.

Transfer the paper and Add a slight excess of 0.1 N carbonate-

free sodium hydroxide ( say 50 ml ). by means of a glass rod.

Disintegrate the filter paper. or pulp Stopper the flask and shake, if all the precipitate

does not dissolve, a further quantity of standard alkali solution shall be added. Dilute to approximately 150 ml, add 5 drops of phenolphthalein indicator, and titrate with standard 0.1 N hydrochloric acid until the pink colour is completely discharged.

3.2.1 Carry out a blank determination using all reagents but without the sample in the same manner and simultaneously.

3.3 Calculation 0.134 9 x ( VI - v;I) Jv

Phosphates ( as P ), percent by weight = ---- CY

Phosphates ( as P,O, ) = 0.308 8 x ( V, - 16,‘) JV

W- , -

IS : 5305 - 1969

where Vr = volume in ml of 0.1 N hydrochloric acid consumed for the

blank determination, V, = volume in ml of 0.1 N hvdrochloric acid consumed by

the excess sodium hydroxide solution,

.N= normality of standard hydrochloric acid, aud W = weight in g of the material contained in the solution

taken for the precipitation.

4. METHOD B - QUINOLINE PHOSPHOMOLYBDATE METHOD

4.0 Outline of the Method- This method involves the formation of phosphomolybdic acid in a solution free from ammonium salts, followed by its precipitation as the salt of quinoline. Finally the quinoline phosphomlybdate is titrated with sodium hydroxide.

4.0.1 General -This method has some advantages over the ammonium phosphomolybdate method, namely, the precipitate is less soluble than ammonium phosphomolybdate, of constant composition, free from absorbed or occluded impurities and free from cations which interfere in the subsequent titration of the precipitate.

The method is applicable in the presence of calcium, magnesium, iron, aluminium, alkali salts, citric acid and citrates. Chromium present up to 18 times the phosphorus content and titanium up to 3.5 times have no effect on the method. The vanadium shall not exceed one-fifth of the phosphorus content. Nitric acid may be substituted for hydrochloric acid. Sulphuric and hydrofluoric acids are deleterious, but the effect of hydrofluoric acid may be avoided by the addition of boric acid. The interference of soluble silicates is avoided by the addition of citric acid with which molybdic acid forms a complex of such stability that its reaction with silicic acid is prevented, whereas the reaction with phosphoric acid proceeds normally. The interference of ammonia is avoided in the same manner.

4.1 Reagents

4.1.X Quinoline Hydrochloride Solution - Add 20 mi of purified quinoline to 500 ml of hot distilled water acidified with 25 ml of concentrated hydrochloric acid conforming to IS : 265-1962*. Cool and dilute to one litre.

4.1.1.1 The quinoline used shall be purified and distilled as follows: s

Dissolve the technical grade quinoline in concentrated hydrochloric acid and add excess zinc chloride solution. This precipitates i

*Specification for hydrochloric acid ( revised j . r

.-

IS: 5305- 1969

quinoline as a complex salt [ ( C,H,N )z.ZnC1,] and in well-deEned crystals. Separate and wash the crysta!s with cold di!ute hydrochloric acid. Regenerate the pure quinoline bv sodium hydroxide solution. Dry and distil to yield pure and distilled quinoline.

4.1.2 Citro-MoEybdate Reagent - prepared as follows:

a) Dissolve 150 g of sodium molybdate ( Na,Mo0,.2H,O ) in 400 ml of water

b) Dissolve 250 g of citric acid in 250 to 300 ml of water and 280 ml of concentrated hydroch!oric acid ( conforming to IS ; 2651962* ). Pour with stirring solution (a) to solution (b), cool and filter through a filter pad. A slight greenish colour is obtained on mixing which may deepen when exposed to sunlight. Add in drops, a O-5 percent ( w/v ) solution of potassium bromate to discharge the colour. Store the solution in coloured, air-tight, stoppered glass bottles in the dark.

4.1.3 Mixed Indicator Solution -Mix 3 volumes of alcoholic phenol- phthalein solution and 1 volume of alcoholic thymol blue solution ( s<e Table 3 of IS : 2263-1962t)

4.1.4 Standard Sodium Hydroxide Solutions - carbonate-free, 0.5 N and O-1 N ( see IS : 2316-1968$ ).

4.1.5 Standard Hydrochloric Acids - 0.5 N and 0.1.N (see IS : 2316-1968$ ).

4.1.6 Dilute Hydrochloric Acid - 10 percent, dilute 100 ml of hydrochloric acid ( conforming to IS ~265-1962” ) to 1 litre with water.

4.2 Procedure -I- Take in a 250-ml conical flask an aliquot of the clear solution of the material, prepared as prescribed in the relevant material specification containing about 50 mg of phosphorus pentaoxide ( 30 mg of P ) present as orthophosphate in about 100 ml ( see Note 1 ). Add 50 ml of citro-molybdate reagent and bring to boil. Add 5 drops of quinoline hydrochloride solution, stirring during the addition. Again heat to boiling and add quinoline hydrochloride solution drop by drop with constant stirring until 2 ml have been added. To the gently boiling solution add the quinoline hydrochloride solution few milliiitres at a time with constant stirring until a total of 60 ml has been added. In this manner, a coarsely crystalline precipitate is produced. Allow to stand on the hot-plate for 15 minutes and then cool to room temperature. Filter through a filter paper or pulp pa.d employing suction and wash the flask,

*Specification for hydrochloric acid ( revised ) . ( Since revised ). tMethods of preparation of indicator solution for volumetric analysis. SMethods of preparation of standard solutions for calorimetric and volumetric analysis

\ revised ) .

7

IS : 5305 - 1969

precipitate and filter with cold water until they are free from acid. Transfer the filter pad and the precipitate to the original flask and rinse the funnel with water into the flask. If necessary, wipe the funnel with a small piece of damp filter paper to ensure complete removal of the precipitate and place the paper in the flask. Dilute to about 100 ml with water. Stopper the flask and shake it vigorously until the pulp and the precipitate are completely disintegrated. Remove the stopper and wash it with water, returning the washings to the flask. From 2 burette add 50 ml of O-5 N standard sodium hydroxide solution, shaking the !?ask during the addition. Shake vigorously until all the precipitstc dissolves ( see Note 2 ). Add 1 ml of mixed indicator solution and titrate the excess of sodium hydroxide solution with 0.5 N hydrochioric acid until the indicator changes from violet to green-blue and then very sharply to yellow.

4.2.1 Carry out a blank determination using all reagents, witliout the sample and using exactly 0.1 N standard sodium hydroxide solution and O-1 N standard hydrochloric acid instead of 0.5 N acid and 0.5 N alkali.

NOTE 1 ---Thr volume should not exceed 100 ml, as any rrduction in the concentratkitn of hydrochloric acid may lead to the formation cf a cream coloured precipitate cf the wrong composition. To avoid such rontaminaticm m the presence of sulohatec, a higher concentration of hydrccilloric acid is necessary.

KOTF. :’ - Examine the disintegrated paper pulp carcfclly for sprcli~ of undissolved precipitate which sometimes dissolve 5: in excess cf sodium hydroxidrr with difliculty.

4.3 Calculation

Phosphates ( as by weight

Phosphates ( as by weight

where

P ), percent 0.059 65 L- p-t - 1::

( L-:, - ;’

- --5---

=; cv, --. 1 --__ -__ 6$’

P,O, ), percent 0.136 5 rl;l - r2 _ i v, ;- v4 ! = _._- 1 L_-__-.-.---_.---- w t; = volume in m! of Cl.5 N sodium hydroxide solution used

with the sample,

V, - volume in ml of 0.5 N hydrochloric acid used with the sample,

P, = volume in ml of 0.1 N sodium hydroxide used jn the blank,

V, = volume in ml of 0.1 N hydrochloric acid used in the blank, and

W = weight in g of the material contained in t!re solution taken for the precipitation.

8

(_,

f

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